The concept of growing sods over plastic sheeting goes back, at least in the United States, to experiments conducted by Henry F. Decker at Ohio Wesleyan University starting in the later 1960's. The concept was first published in an April 1975 newspaper article in the Columbus (Ohio) Dispatch from which it was widely distributed around the U.S. and into several other countries by the Associated Press. A more extensive article also appeared in the June 1975 trade magazine "Weeds, Trees, and Turf" (now Landscape Management). Later phases of the research were supported by grants from the National Science Foundation.
In these early experiments it was shown that it was feasible to grow grass sods over a root impervious surface, typically plastic sheeting, using various contrived growing media in place of topsoil. There were several distinct advantages to growing sods in this manner. The primary rooting of the grasses could be used to knit the sod and could be maintained intact in the final product, unlike in conventional sodding where the primary rooting is cut off when the sod is harvested and then has to be regenerated when the sod is placed on its new site. Topsoil as the growing medium could also be replaced by a wide range of materials typically known to be waste materials. In addition, the sod is typically lighter as compared to mineral soil-grown sods. Moreover, since the primary rooting will be used to bind the sod, sod can be grown and harvested much more quickly, often in just a few weeks. These methodologies of "manufacturing sods" lend themselves to the harvesting and handling of sod in big rolls, often four feet wide by seventy feet or more long (Decker U.S. Pats. Nos. 4,986,026 and 5,177,898).
A wide variety of materials were tested as growing media in the early Ohio Wesleyan experiments and were listed in a 1972 Document Disclosure (012097) followed a year later by a patent application Ser. No. 371,462. These materials included organic wastes such as digested or composted garbage, leaves, and sewage sludge; seed or fruit hulls; spent tea leaves; loose and compressed cellulose fibers; wood chips and bark; sawdust, peats, and manures of various kinds; ground corn cobs; various grades, densities, and thicknesses of plastic foams; and many kinds of mineral matter including sand in varying grades, calcined clay, diatomaceous earth, and the expanded micas, such as perlite or vermiculite.
Later experiments included spent mushroom soil, straw, and composted sewage sludge, yard waste, and animal manures (Decker U.S. Pat. Nos. 4,986,026 and 5,177,898). Subsequent patents have also used rice hulls (Rogers et al U.S. Pat. No. 4,720,935), mushroom soil (Walton U.S. Pat. No. 4,934,094), conifer bark (Chamoulaud U.S. Pat. No. 4,232,481), straw (Heard U.S. Pat. No. 4,716,679), sand (Egan U.S. Pat. No. 5,301,446), and others. Other methods of production over plastic include using various types of nettings, geotextiles, polypropylene covers, burlaps, and other fabrics all of which are useful in specialized cases. In particular, composted sewage sludge and composted yard waste or the two of them in combination have proven to be very effective media and they are both plentiful, inexpensive, easy to handle, and rich in nutrients.
Despite the many apparent advantages of growing sods over plastic, there were several major problems that had to be solved before the innovative concept had any economic significance. These problems have been reviewed by Decker in U.S. Pat. Nos. 4,986,026 and 5,177,898. Probably the most difficult of these problems, especially to the east of the Rocky Mountain rain shadow, is that of severe thunderstorms which can quickly wipe clean a thin patina of growing medium placed unprotected on a smooth sheet of plastic. This common act of nature has made most patents in this genre, including the early ones by Goodall (G.B. 1,290,338), Dawson (G.B. 1,455,133), Loads (U.S. Pat. No. 3,863,388), Blackburn (U.S. Pat. No. 3,890,739), Schneider (U.S. Pat. No. 4,225,359), and others, impractical and uneconomical for large scale planting typical of U.S. sod production.
Solving the problem of thunderstorms figured prominently in the early history of soilless sod technology. The Decker patents teach the use of various mulches to form mulch/media/matrixes, some types of which are surprisingly resistant to laminar flow and hence to sheet erosion. In effect the mulch forms a continuum over the plastic into which the growing medium is infiltrated. If this "3M system" is carefully constructed, media as this as 1/4 to 3/8th inch can be stabilized in severe thunderstorms which is a significant improvement in the stability of soilless sods.
All of the early work on soilless sods of which I am aware was done with seeded, largely cool season varieties of turfgrasses. I first began experimenting extensibly with warm season, vegetative material in Ohio in the summer of 1991 (Document Disclosures 294725 and 337067). Essentially, the seed in the mulch/medium/matrix was replaced with stolons or sprigs, and it was possible to produce high quality warm season sods in just a matter of a few weeks.
Different types of mulches were also tested including wood shavings, cocoa shells, shredded cypress bark, and pine needles; and some different growing media including composted yard mulch from Hilton Head, S.C., and crushed cocoa shells.
In the fall of 1993, RapidTurf, Inc. of Rincon Ga., hired me as a consultant to see if any of the principles learned from the "3M system" above could be applied to the production and stabilization of greens quality sods grown over plastic in a sand medium. RapidTurf was experiencing a common problem, namely, the integrity of their growing medium, which was a thin patina of USGA spec sand over plastic into which they planted sprigs or stolons, was being destroyed by the heavy thunderstorms characteristic of southeastern U.S. summers. No provision had been made for this environmental condition in their technique, nor was an adequate solution included in their recent U.S. patent (U.S. Pat. No. 5,301,446). They were losing too much of their crop to severe thunderstorms.
The present invention solves the above problem (presented in Document Disclosures 342627, 363575, and 365091)and provides an efficient and reliable method for planting and, at the same time, stabilizing grass sods growing over plastic sheeting.